Camshaft phasers (“cam phasers”) for varying the timing of combustion valves in an internal combustion engines are well known. A first element, known generally as a sprocket element, is driven by a chain, belt, or gearing from an engine's crankshaft. A second element, known generally as a camshaft plate, is mounted to the end of an engine's camshaft.
U.S. Pat. No. 7,421,990 B2, herein incorporated by reference, discloses an eVCP comprising first and second harmonic gear drive units facing each other along a 25 common axis of the camshaft and the phaser and connected by a common flexible spline (flexspline). The first, or input, harmonic drive unit is driven by an engine sprocket, and the second, or output, harmonic drive unit is connected to an engine camshaft.
A first drawback of this arrangement is that the overall phaser package is undesirably bulky in an axial direction and thus consumptive of precious space in an engine's allotted envelope in a vehicle.
A second drawback is that two complete wave generator units are required, resulting in complexity of design and cost of fabrication.
A third drawback is that the phaser has no means to move the driven unit and attached camshaft to a phase position with respect to the crankshaft that would allow the engine to start and/or run in case of drive motor power malfunction. eVCP have been put into production by two Japanese car manufacturers; interestingly, these devices have been limited to very low phase shift authority despite the trend in hydraulic variable cam phasers (hVCP) to have greater shift authority. Unlike hVCP, the prior art eVCP has no default seeking or locking mechanism. Thus, phase authority in production eVCPs to date has been undesirably limited to a low phase angle to avoid a stall or no-restart condition if the rotational position of the eVCP is far from an engine-operable position when it experiences eMotor or controller malfunction.
What is needed in the art is an eVCP including means for the eVCP to mechanically return to a default engine-operable position in the event of eMotor malfunction.
It is a principal object of the present invention to return an eVCP to a predetermined ‘default’ position in the event of eMotor malfunction.